This invention relates to coated multilayer plastic substrates having an excellent balance of adhesion and gasoline resistance.
It is often difficult to coat plastic substrates because the inherent crystallinity of such polymers prevents adequate bonding to many coating compositions. This is particularly true when the plastic substrate is also non-polar, as in the case of polyolefin substrates. Primers based on polypropylene graft copolymers have been used with some success to enhance adhesion, but, unfortunately, the adhesion is still inadequate for some applications. In particular, the coating compositions of the prior art have not provided an adequate combination of adhesion, weatherability, and gasoline resistance. Such properties are desirable when the coated substrate is designed to be used in an outdoor setting in which it is exposed to the elements, especially in automotive assemblies. For example, in Japanese Patent Application Publication Kokoku 4-72847, a coated polyolefin substrate is disclosed wherein a primer layer composed of a crosslinked chlorosulfonated, carboxylated polyolefin is used. Although this provides some degree of enhanced adhesion and gasoline resistance, it is inadequate for certain applications which require superior adhesion performance.